Allocate Any Extended Memory (Function 89h)

        ARGS:   AH = 89h
                EDX = Amount of extended memory requested, in Kb.

        RETS:   AX = 1 if the block is allocated, 0 if not
                DX = Handle to allocated block.

        ERRS:   BL = 80h if the function is not implemented.
                BL = 81h if a VDISK device is detected.
                BL = A0h if all available extended memory is allocated.
                BL = A1h if all available extended memory handles are in use.

This function is similar to the existing Allocate Extended Memory,
except that it uses a 32-bit instead of a 16-bit value to specify the
amount of memory requested.  It allocates from the same memory and
handle pool as the current function.  Since it requires a 32-bit
register, this function can be supported only on 80386 and higher
processors, and XMS drivers on 80286 machines should return error code
80h.

Note: This function is new to version 3.0